Datepicker fix for other locales than en_US on ActionPlanCreation

[ghost]

The JS file ActionPlanCreationScripts contains logic which expects all dates to be formatted MM/dd/yyyy. In European countries e.g. the typical format is dd/MM/yyyy.

The date picker then is completely screwed up. It is not displayed at all or the target date is not shown.

Reproduce: Set locale (not language) to e.g. German or Spanish and create a new action plan e.g. on Contact. Check the DatePicker.

This fix now supports dates in other locales than en_US. The original code did some hard coded parsing and expected all dates to be formatted MM/dd/yyyy. For other locales which format dates e.g. dd.MM.yyyy, the code failed and the DatePicker in the "days after" column did not show the target dates or failed to open.

It makes usage of the DateUtil javascript class in main.js, thus the methods are not documented but as the AP code uses the DatePicker already (which depends on the DateUtil class too) I think it's an acceptable risk compared to the previous hard coded routines that are known to fail in most of the countries.